This invention is directed generally to television signal distribution systems and particularly to systems using a cable to distribute multiple video signals to a plurality of video devices. This invention relates more particularly to apparatus and methods for connecting a video device to a single uninterrupted cable and reducing the disturbance caused by connecting the video device to the cable.
Most commercial signal distribution systems use a high-powered amplifier to drive signals down a single cable with signal taps used as drops to various outlets. To minimize impedance mismatches, the signal attenuation of the taps to each drop is high, on the order of 12 to 20 dB so that one or more very powerful and costly amplifiers are required to maintain the signal at an acceptable level.
Most residential cable TV distribution systems have a main cable that delivers video signals to the customer""s home. Signal splitters are then used to connect xe2x80x9chome runxe2x80x9d cables between the main cable and video outlets. The result is sometimes referred to as a xe2x80x9cstarxe2x80x9d network. Although the splitters supply the necessary impedance matching for each run, the total signal loss through the splitters often exceeds 12 dB, again requiring one or more expensive amplifiers.
There is a need in the art for a technique for allowing video devices to be connected directly to a single cable, thereby eliminating the signal losses associated with taps and/or splitters, while not disturbing the system""s impedance match.
The present invention provides a video interface circuit that reduces loading losses when a video system component, such as a television receiver, is connected to a cable network.
The present invention includes an interface circuit connected to a signal tap in the cable for receiving video signals therefrom and producing an amplified video signal for delivery to the video device. An amplifier circuit and a passive positive feedback circuit are connected between the amplifier circuit output and the tap for introducing an amplified video signal into the cable network. The amplifier is capable of amplifying signal frequencies of up to 10 GHz or more so that the signal fed back into the cable does not cause signal distortion in the cable.
The interface circuit according to the present invention preferably comprises a first transistor circuit connected to the tap for receiving video signals therefrom. The invention preferably further includes a second transistor circuit arranged to receive signals from the first transistor circuit and produce an amplified video signal. The feedback circuit is connected between the second transistor circuit and the tap for introducing the amplified video signal into the transmission cable.
The feedback circuit preferably comprises a passive network connected between the amplifier output and the tap. The feedback circuit preferably provides a gain of 12 to 15 dB in the video signal that is introduced into the coaxial cable at the tap.
An appreciation of the objectives of the present invention and a more complete understanding of its structure and method of operation may be had by studying the following description of the preferred embodiment and by referring to the accompanying drawing.